When I served in the army as an artillery scout, we indeed had to take magnetic deviation (declination) into account (well, it is obviously not indifferent where you shoot with a 152 mm cannon over a 25 km distance of course).
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I really doubt that such a small deviation would have any serious affect on how a model is placed on GE. Also, it changes from place to place and not even only up to the geographic location relative to the geographical and magnetic North but a bunch of other things can affect it.
Is it really worth the hassle? What project do you have where it would be so important?